This invention relates to improvements in devices to control the temperature of fluids administered to patients.
Patients often require administration of fluid and blood products at or near body temperature in order to prevent hypothermia from occurring. Such fluid administration is also known as intravenous (I.V.) fluid administration. This is especially important during anesthesia, surgery, shock and trauma when body temperature may be reduced by exposure or by interference with the body""s thermoregulatory mechanisms. Hypothermic patients often experience uncontrolled shivering. Patient recovery is often complicated and extended by hypothermia.
Patients requiring blood are often in a state of circulatory shock. Blood is generally delivered from blood banks cold and is typically not adequately warmed to body temperature prior to administration due to time limitations of emergency circumstances. This situation compounds the problems facing the patient. Patient mortality and morbidity could be substantially reduced by delivery of blood and other fluids at proper body temperature.
Current methods of controlling the temperature of intravenous fluids and blood are in-line fluid warmers and external bulk fluid warmers. In-line fluid warmers heat fluids by applying heat directly, using a heating element, to fluid as it passes from the fluid reservoir to the patient. These heaters are located a substantial distance from the patient and temperature loss is substantial by the time the fluid reaches the patient.
External bulk fluid warmers heat the I.V. fluid bottle or bag prior to administration to the patient. The bottles or bags are removed from the heaters and placed next to the patient on an I.V. stand as they are needed. The bottle or bag is attached to a fluid administration set, consisting of a drip chamber, fluid administration (I.V.) tubing, roller clamps and I.V. cannula. The fluid passes from the reservoir to the patient through the fluid administration set under the force of gravity. As the fluid passes through the administration set, it loses heat. This temperature attenuation is exacerbated by low flow rates because of increased fluid dwell time in the I.V. tubing. Because of its long length and corresponding large surface area, substantial heat loss to the room occurs in the I.V. tubing. In addition, the warm fluid bag or bottle cools down over time and will, given enough time, eventually reach ambient room temperature.
Although insulated lines help the problem, temperature losses remain substantial. Typical warming systems are cumbersome, bulky and not sufficiently user-friendly for frequent use. The limitations of existing technology force clinicians to deliver cool and unregulated intravenous fluids and blood to their patients. Although not a preferred practice, there is no convenient method for regulating the temperature and delivery of intravenous fluids and blood products to patients.
The present invention discloses an improved device and method for controlling the temperature of fluids delivered to a patient. The invention is a system that ensures that fluids delivered to the patient reach the patient at the desired temperature, generally body temperature or 37.0 degrees centigrade.
A temperature measurement probe is located at the end of the I.V. tubing nearest the patient. This temperature measurement is taken near the patient and the information is fed back through wires or by wireless methods to a circuit that controls an in-line heating element that heats the fluid. In this way, temperature losses in the I.V. tubing may be compensated by overheating the fluid so that it reaches the patient at the desired temperature.
In another embodiment of the invention, the feedback from the temperature probe is transmitted through wires, which are integral to the I.V. tubing. The transmission line wires may be embedded or co-extruded, for example, within the tubing. A connector is attached to the transmission line wires in the tubing. This connector allows transmission of information to the controller through electrical leads, attached to the connector. In this manner, cost is reduced and the system is simplified so that no additional components need be set up by the nurse or medical practitioner.
In yet another embodiment, insulated tubing may be used to minimize heat loss in the I.V. tubing and, thus, minimize the amount of overheating required of the in-line heater.
In the preferred embodiment, the in-line heating is accomplished by pumping heated fluid through channels or lumens that run parallel and adjacent to the fluid administration channel in the I.V. tubing. In this way, the heating is distributed along the length of the I.V. tubing so temperature gradients are reduced. This embodiment requires a fluid pump, heater, controller, and temperature probe as well as heat exchange tubing, a heating manifold and at least one fluid shunt.
In yet a further preferred embodiment, the heating channels are located radially exterior to the fluid administration channel. In this way, the heating channels not only heat, but they also buffer, or insulate, the fluid administration channel from ambient temperatures surrounding the I.V. tubing.
In another embodiment, the heating channels, manifold, shunt and delivery tubing are pre-filled with heat exchange fluid so that messy filling and handling are not required.
In yet another preferred embodiment, an additional insulation layer may be disposed radially outward of the heating channels to minimize heat loss to the environment.
In yet another embodiment, the distributed heating is accomplished by resistive or Ohmic heating of a metal or ceramic element that runs along the length of the I.V. tubing.
A key advantage of this system is that fragile fluids such as blood and blood products are not overheated prior to delivery to the patient. Another advantage of the system is that it may be inexpensively fabricated and it may be provided in a convenient configuration that encourages its use. The set allows for disposability, pre-sterilization, low cost and convenient operation.